Multiple target automatic trackwhile-scan radar



Aug. 21, 1962 F. D. covELY, 3RD

MULTIPLE TARGET AUTOMATIC TRACK-WHILE-SCAN RADAR Filed Aug. 25, 1955 9 Sheets-Sheet 1 lil t lsv/Z Avrai/JH Aug. 21, 1962 F. D. covELY, 3RD

MULTIPLE TARGET AUTOMATIC TRACK-WHILE-SCAN RADAR Filed Aug. 25, 1955 9 Sheets-Sheet 2 INVENTOR. FAM/vx Q fovagsi. BY

j@ if Aug. 2l, 1962 F. D. covELY, 3RD

MULTIPLE TARGET AUTOMATIC TRACK-WHILE-SCAN RADAR Filed Aug. 25, 1955 9 Sheets-Sheet 3 lllll ir TURA/EY Aug. 21, 1962 F. D. covELY, 3RD 3,050,722

MULTIPLE TARGET AUTOMATIC TRACK-THILE-SCAN RADAR Filed Aug. 25, 1955 9 sheets-sheet 4 Aug. 21, 1962 F. D. covELY, 3RD 3,050,722

MULTIPLE TARGET AUTOMATIC TRAcK-muLE-SCAN RADAR Filed Aug. 25, 1955 9 Shets-Sheet 5 INVEN TOR. @m1/K Con/L rsf@ Aug. 21, 1962 F. D. covELY, 3RD

MULTIPLE TARGET AUTOMATIC TRACK-WHILE-SCAN RADAR Filed Aug. 25, 1955 9 Sheets-Shes?l 6 dwwwmkiwwwmul Aug. 21, 1962 F. D. covELY, 3RD

MULTIPLE TARGET AUTOMATIC TRACK-WHILE-SCAN RADAR Aug. 21, 1962 F. D. COVELY, 3RD 3,050,722

MULTIPLE TARGET AUTOMATIC TRACK'VIIIL-SCAN RADAR Filed Aug. 25, 1955 9 Sheets-Sheet 8 IN V EN TOR. Ffm/K (0V/:1); 3K0.

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3,@,722 Patented Aug. 2l, 1962 3,050,722 MULTIPLE TARGET AUTOMATIC TRACK-- E-SCAN RADAR Frank D. Covely 3rd, Haddonteld, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Aug. 25, 1955, Ser. No. 530,485 21 Claims. (Cl. 343-11) 'Ihe present invention relates to the art of radar detection and in particular to an improved radar system of the so called automatic track-while-scan type. An automatic track-while-scan (ATWS) radar is one which continuou-sly scans a given volume of space and continuously, automatically provides data as to the positions of one or more targets in this Volume of space.

The straightforward approach to ATWS radar is to employ a single radar unit having a pencil type beam. This beam is continuously nodded through a given angle of elevation and continuously scanned, at a slower rate, through 360 in azimuth. The polar coordinate information received as to the slant ranges, azimuth angles and elevation angles of targets in the scanned volume of space may then be stored and the stored data subsequently periodically corrected to maintain it up-to-date. Alternatively, it may be desirable to convert the polar coordinate information to rectangular coordinate information before storage and subsequent periodic correction. The rectangular coordinate information is in the form X, Y, Z; Z designating target altitude, and X and Y designating the respective geographical coordinates of the target in a horizontal plane.

T-he diiculty with the straightforward approach is that the rate at which the radar unit receives information from any one of the targets is -much too slow. Since the periodic correction of stored data can lbe no more rapid than the information rate, the stored data becomes stale between correction intervals and, for many purposes, absolutely useless.

The serious limitations of the straightforward approach can best be illustrated by specic example. volume of space of interest extends 50 miles from a ground ATWS radar. Assume also that the radar has a pencil type beam 0.755 in elevation and 2 in azimuth (this corresponds to a known radar of practical design). Finally, assume that the beam is continuously nodded through an angle of 40 in elevation at a relatively rapid rate (say roughly l nod per second) and continuously rotated through 360 in azimuth at a slower rate. One complete antenna cycle 'for full coverage of the volume of space of interest has been found toy require roughly l0 minutes. The hits per radar beam width under these conditions i-s 15 which, it has been found, provides adequate `detection probability.

Faster scanning rates are, `of course, possible but only at some cost in performance. If the antenna elevation nod frequency, for example, increases past a certain ligure, certain targets might be missed completely. The reason is that when the scanning rate is increased with a given pulse repetition rate, the number of interceptions of the pulse by the target is reduced. Due to the characteristic fading of radar returns, a number of hits is required to attain reasonable assurance of detection, particularly at long ranges where targets are easily confused with noise.

If the antenna scanning period is l0 minutes, the infomation period is minutes and this, of course, is entirely inadequate. If the stored data is corrected only once every l0 minutes a 200 knot aircraft may move more than 30 knots between scans and a 600 knot aircraft may move 100 knots between scans. fIn certain ATWS radar application -such as, for example, aircraft trailic control,

Assume the ground controlled aircraft interception and the like, where fractions of a vmile may be important such a system would, at best, be entirely inadequate-even for slow moving aircraft.

The problem then is to increase the information rate in an ATWS radar system. One solution is employ two or more radars of the type described above assigning to each only a sector o-f the 360 to be covered. This, however, would be an extremely expensive solution and accordingly, not practical. If, for example, it was desired to reduce the information period to 3() seconds, 20 radar units would be required, each scanning a different 18 azimuth sector.

It is a general object of the present invention to provide an improved ATWS radar system w-hich has the important advantage of supplying information as to the 1ocation of targets at a relatively rapid rate.

It is another object of the invention to provide an improved arrangement for correlating data as to target positions received from two or more radars which are not synchronized with one another.

This invention proposes the use of at least two radars. 'The first scans continuously through 360 in azimuth alone and employs a beam having generally a fan-shaped elevation pattern. The second scans through a predetermined elevation sector and employs a narrow, pencil type beam pattern. Means are provided for rapidly slewing the second radar in azimuth 4from target-to-target. 'I'he second radar nods only through the sectors of elevation including the targets and provides elevation data as to the locations of the targets. The information received bythe two radars is then correlated by a novel arrangement to be described in more detail later, stored, and periodically corrected. In one form of the invention, the polar coordinate information provided by the two radars is converted to rectangular coordinate information before storage and subsequent correction.

The invention also includes an arrangement for slewing the second radar, hereinafter termed a height-finder radar, to the different known azimuth target positions in azimuth sequence, regardless of the -order of acquisition to targets. This substantially increases the rate at which the ATWS radar system supplies information. The information rate may be `further increased, if necessary, by increasing the number of height-finder radars.

It has been previously mentioned that the stored data correction period for an ATWS radar system employing a single radar which both nods in elevation and scans in azimuth is l0 minutes per target. If two such systems are employed, each covering a azimuth sector, the period is reduced to 5 minutes per target. The system is capable of handling a large number (25 or more) targets. With the ATWS radar system of the present invention, as described above, employing one azimuth radar unit and one height-finder radar unit, the data correction period may be reduced to 30-40 seconds or less per target with 25 target-s being tracked. For more or fewer targets the period of correction may be respectively increased or decreased proportionately.

The invention will be described in greater detail with reference to the accompanying drawing in .which similar reference characters refer to similar elements, and in which:

FIGURE l is a block circuit diagram of a preferred embodiment of the invention utilizing a Search radar and a height-finder radar in combination;

FIGURES 2a and 2b comprise amore detailed, circuit diagram, partially in block and partially in schematic form, of the preferred embodiment shown in FIGURE 1;

FIGURE 3 is a more detailed block and schematic circuit diagram of a portion of the arrangement shown in FIGURE 1;

FIGURE 4 is a sketch of a negative analog pulse;

FIGURE 5 is a schematic circuit diagram of an arrangement for producing negative analog pulses;

FIGURE 6 is a drawing of a coordinate resolver or so called joy-stick control used in the present invention;

FIGURE 7 is a schematic diagram of a comparison, gating and height-storage circuit which is employed in the present invention;

FIGURE 8 is a 4block and schematic circuit diagram of an embodiment of the invention in which a storage tube is employed;

FIGURE 9 is a schematic circuit diagram of a pulsetype range coordinate resolver; and

FIGURE 10 is a block and schematic circuit diagram 0f an arrangement for slewing a height-finder radar antenna from target-to-target in azimuth sequence.

The system of the invention will rst be described in brief by reference to one specific embodiment. Detailed discussion of various circuit features follows later.

Assume first that the maximum range of interest is 50 miles. (Other smaller or greater ranges are of course possible and within the scope of this invention.) At this range it requires about 500v microseconds for a pulse of electromagnetic energy to travel to a target and return to the point of transmission. (The last mentioned number and others to be used in this discussion are approximate, however', the approximations in no way affect the validity of conclusions which will be drawn.) It is usual design practice to allow a recovery time of about this same interval (500 microseconds) for this range so the pulse repetition frequency for the system under discussion is a maximum of 1000 pulses per second. With a radar beam pattern which is generally fan shaped or c0- secant squared shaped in the elevation plane and 1 in the azimuth plane between half power points, a minimum of 360 pulses would be required to cover 360 of space, in azimuth, relative to the r-adar. Thus, in principle, a radar of this type can rotate 360 in azimuth in 0.36 seconds. In practice, about 10 to l5 pulses are used per beam width to increase the detection probability. This results in a rotational period on the order of 3 to 5 seconds.

One embodiment of the present invention employs a radar of the above type for its azimuth-range radar (also termed two-dimensional radar elsewhere in this application).

The height-finder radar of the above embodiment of the invention may be of the type already described in brief above. The beam is 0.755 in elevation and 2 in azimuth. The range is 50 miles. The nodding rate is roughly once per second for a 40 sector of elevation. The beam can be slewed through 180 from start-to-stop in 5 to l0 seconds. The slewing speed can be increased substantially, if necessary, by using larger powered antenna motor drives.

According to the present invention, the azimuth-range radar continuously scans in `azimuth and provides information as to the X, Y, rectangular coordinates of a target. The height-finder radar is slewed from target-totarget in azimuth sequence and provides information as to the Z rectangular coordinate of the target. Assuming a slewing time of 5 to l0 seconds for 360 of azimuth rotation of the height-nder radar (according to the size of the drive motors employed) the information period of the height-finder radar is roughly 1 second times n plus 5 to l0v seconds, where n is the number of targets. For targets, the data period is 30 to 35 seconds as contrasted to 5 minutes for the prior art system. With more powerful drive motors, the information period can be lessened even more.

The invention includes the means for correlating the X, Y, information supplied by one radar with the Z information supplied by the other radar. This will be described in greater detail below.

4 r. PREFERRED EMBODIMENT Referring to FIGURE l, a two-dimensional search radar 11 provides slant range (R) and azimuth angle (0) data to the analog-forming circuits 113. These convert the range and azimuth data into sawtooth voltage analogs of the X- and Y-coordinates (which may be in terms of east-west and north-south position if the radar is so oriented) of the geographical location with respect to the radar 11 of the transmitted radar pulse. An analog voltage is a voltage whose amplitude represents some other quantity. (The specific operation and circuits of a typical two-dimensional ATWS radar and more detailed descriptions of analog voltages are described below.) The output of the analog-forming circuits 113 is applied to the X- and Y-store circuits 31-37, 31a-37a. For convenience, only two pairs of X-Y stores are illustrated, namely the Xland Yl-stores 31 and 37 associated with a first ta-rget and the X2- and YZ-stores 31a .and 37a associated with a second target. Each pair of X-Y stores store the respective X- and Y-analogs of a specific target.

The outputs of the pairs of X-Y stores are impressed upon dilierent height comparators, the structure and mode of operation of which will be explained later. Each height comparator is coupled to a height gate-and-charge circuit and a height store circuit. For example, the X1- store 31 and the Yl-sto-re 37 are coupled to the Hl-comparator 123, which is coupled to the Hl-gate-and-charge circuit 124, which, in turn, is coupled to the Hl-store 31b. Thus, one complete set of stores comprises an X, a Y-, and an H-store.

The height-finding radar 128, whose antenna scans independently of the scanning of the antenna of the search radar 11 (although the antennas may be arranged to scan in azimuthal synchronism), provides range and height data to a height resolver 130, which generates a pulse (I-I-analog pulse) having an amplitude proportional to the elevation angle of the target from which the height data is being obtained.

In addition to this, the height-finding radar 128 continuously supplies a range sweep sawtooth voltage to the range resolver 12b which resolves this sawtooth into two component sawtooth voltages corresponding to the X- and Y-components of position of the radiated pulse as it travels away from the radar. These resolved range-sawtooth voltages are applied in common to all the height comparators where they are compared with the X- and Y-analogs from the X- and Y-stores. When the instantaneous values of the resolved range sawtooth voltages are approximately equal -to a pair of X- and Y-analogs, the H-comparator to which that pair of X- and Y-analogs is applied, produces a gating pulse which is impressed upon its associated H-gate-and-charge circuit. The gating pulse places the H-gate-and-charge circuit, which is normally cut off, in an operative condition, thereby permitting the amount of current flow through the H-gate-andcharge circuit to ybe determined by the amplitude of the H-analog pulse which is also applied to the H-gate-andcharge circuit.

The amounts of current ow through the H-gate-andcharge circuits determine the amounts of charge stored in the respective height stores associated therewith. Thus, height data for a given target is stored in the height store coupled to the range stores associated with that given target. Since the incoming data is continuously derived and since the comparison of the incoming data is simultaneously and continuously performed for all pairs of stores, automatic storage and correction of data for a plurality of targets (as many as there are sets of stores) may be effected.

This system operates automatically provided that X- and Y-data for comparison purposes is already stored in at least one pair of X- and Y-stores. Height data `for its corresponding target will then be impressed upon the tion of the radar antenna .153.

proper height store. However, to begin the automatic operation, X- and Y-data must initially be inserted in the X- and Y-stores and this is accomplished by the target acquisition circuits 126 described in detail later on.

FIGURES 2a and 2b together comprise a more detailed drawing of the system illustrated in FIGURE l. Components of the twoedimensional radar 11, the height finding radar -128 and the target acquisition circuits 126 are shown as well as the optical arrangement of the monitor display device 92, the dichroic mirror 91 and the radar display device 9i). A more detailed explanation follows.

Pulse Former The operation of a pulse-type searoh radar 11 (FIG. 2a) -is well known and will only be sketched briey herein. A timer 150, which may be a blocking oscillator or other type of pulse-generating circuit, delivers trigger pulses to the transmitter 151 which generates high-power pulses of high-frequency electro-magnetic energy. These pulses are applied through a duplexer 152, whichI may be a gas-lilled, transmit-receive switch, to the antenna 153, which radiates the energy into space. The antenna is rotated azimuthally by means of the antenna azimuth drive mechanism 154, which may be a motor.

If a radiated pulse strikes a target, such as an aircraft, it may be reflected back to the antenna 153. If so, it is impressed upon the duplexer 152, whence it is applied to the receiver 155', where it is amplified and detected.

The echo pulse is then fed to a pulse former v13, which may be a blocking oscillator or the like. The pulse Iformer 13 serves to reform the echo pulse into a pulse having a steeply rising front and a predetermined constant amplitude, so that circuits which are intended to respond to, or be` synchronized by, the stimulus of the echo pulse will be actuated in a positive manner which does not vary from pulse to pulse.

Range Resolvers 'I'he range sawtooth generator 156 can be any one of a number of well-known circuits which produce a linear rise in voltage with time. The trigger pulses from the timer 150 are employed to initiate the saiwtooth waves. The `output of the range sawtooth generator 156, called the range sweep voltage or range sawtooth, is sup-plied to the sweep deection coil 157 of an electro-magnetic cathode-ray display device 90 to sweep the electron beam radially outward from the center to the periphery of the screen of display tube 90 in time synchronism with the radiated pulse, so that the position of the beam at any given instant is proportional to the distance the radiated pulse has travelled from the antenna 153. Since the position of the electron beam depends upon the amplitude of the range sawtooth volt-age at that instant, `the slant range of the radiated pulse (and, therefore, of any target it strikes) can be determined from the amplitude of the range sawtooth.

To completely locate the geo-graphical position of the radiated pulse in polar coordinates in relation to the radar 11, it is also necessary to take into account the azimuthal position of the radiated pulse, which in turn depends upon the angular displacement of the antenna 153` with respect to a fixed azimuthal reference point (assumed to be north herein). Each succeeding radial sweep (which shall also be referred to herein as a strobe or strobe line) is slightly displaced from the previous one by rotating the sweep coil 157 in synchronism with the azimuthal rota- 'I'he resultant scan is called a PPI (plan-posinon-indicator) scan. Echoes displayed on a display scope utilizing such a scan are completely located with respect to the radar 11 in terms of slant range and azimuth.

The process of completely locating the geographical position tof the radiated pulse in cartesian coordinates, can be accomplished by applying the range sawtooth to a range resolver 12 which separates the sawtooth into two component sawtooth voltages, the east-west component hereinafter called the X-sawtooth 55, and the north-south component hereinafter called the Y-sawtooth 56. Range resolvers and the process of determining the position of a radar target by resolving a range sawtooth voltage into its X- and Y- components `are well-known and a description of several types of resolvers is given in Radar System Engineering, volume I, MIT Radiation Laboratory Series, Section 13-4. The specic resolver 12 used here is a synchro having two output stator coils in quadrature and a rotor coil mechanically coupled to the rotating antenna 153. The input to the rotor coil is the range sawtooth voltage and the outputs of the range resolver 12 are synchronous sawtooth voltages 55 land 56, the relative amplitudes of which vary with the sine and cosine of the angle of rotation (6) of the radar antenna 153. The amplitudes of the X- and Y-sawtooths at the time the echo pulse is received may be utilized to determine the position of the target.

Analog Pulse Generator Referring to FIG. 3, the X- and Y-sawtooth voltages 55 and 56 are impressed upon the X-bus bar 16 and bus bar 17, respectively, and then coupled -to the X-analog pulse generator 14 and Y-analog pulse generator 15, respectively.

An analog voltage is defined herein as a voltage whose amplitude represents some other quantity. At any given instant, the amplitude of the X-sawtooth voltage 55 represents rthe east-west position of a target reflecting a transmitted pulse with respect to the location of the yantenna 153, and, therefore, the X-sawtooth voltage 55 is an analog of the east-west position of said target at that instant. The X-sawtooth voltage 55 is hereinafter interchangeably referred to as the X-an-alog voltage 55.

A negative analog pulse is defined herein as a pulse whose amplitude, as measured from zero or some other reference voltage, is the negative tof some analog voltage. Thus, in FIGURE 4, a negative analog pulse 57 is shown, having an amplitude NA which is the negative of the positive analog voltage indicated by the dotted line, the amplitude of which is indicated by the letter A. It will be noted that, in this particular case, the base line S2 of the pulse 57 does not coincide with 'the zero voltage level but is even more negative than the amplitude NA of the negative analog pulse 57. This is necessary because the ibase voltage i-s used as a bias for tubes 34 and 36 (FIG. 3) as will be described later.

Continuing with FIGURE 3, only Ithe parts of the system concerned with operations upon the X-analog voltage, or X-s-awtooth, will be described in det-ail, since they are substantially identical with the analogous elements of the system concerned with the Y-analog voltage, or Y- sawtooth.

A circuit for forming such a negative analog pulse is shown in FIGURE 5. The analog voltage, X-sawtooth voltage 55 from the X-bus 16, is impressed on the control grid of an electron tube 6d operating as an ampliiier with a gain of approximately unity by virtue of the relative proportions of resistors 61 and 62. The waveform 85 on the plate of tube 6G is a negative-going replica of the impressed sawtooth 55. A D.-C. restorer circuit comprisi-ng condenser 63, diode 64, and resistor 65 establishes ground potential, or zero volts, as a base voltage from which each negative excursion of the sawtooth originates. This wave 86 is then impressed upon a cathode vfollower tube 67 which operates without plate voltage most of the time.

The ygrid current of the cathode follower tube 67 is limited by grid resistor 66, and the cathode is returned throfugh resistor 68 to a negative supply voltage which establishes the base line 82 of the negative analog pulse 57 shown in FIGURE 4. The pulse itself is formed by applying plate voltage to the cathode follower tube 67 at the proper time, this action being accomplished lby means of a delay-linc pulse generator stage 72 which is triggered on `by pulses 87 from the pulse former 13 (FIGURE 3) and is cut oi by the removal of its plate voltage upon termination of the pulse generated by the delay line 73. Thus, the amplitude NA of the negative `analog -pulse 57 which is obtained across cathode resistor 68 corresponds to the value of the X-sawtooth at the instant an echo pulse is received, and therefore corresponds to the X-component of the spatial location of the radars target. This negative analog pulse y57 is then impressed upon the Xp-hus 1S.

The manner in which a pulse is formed by the gas tube '74 and the delay line 73 in conjunction with the timing pulse from the pulse former 13 is explained in Waveforms, Volume 19, Radiation Laboratory Series, pages 239-241.

Returning to FIGURE 3, the X-sawtooth voltage S is coupled from the X-bu-s 16 to the X-analog pulse generator 14, whose output, negative X-analog lpulses 5-7, is impressed upon the Xp-bus 1-8. Thus the value of the Xanalog pulse 57, measured from zero, is indicative of the X-position of the target, whose echo initiated the formation of the X-analog pulse 57.

Store Circuits It will be assumed that the radar is in the process of tracking a target and, therefore, that the X-storage condenser 32 of the Miller Integrator of Store Circuit 31 has a charge corresponding to la previous X-coordinate of Ithe position of the target (how the charge is initially inserted will be explained later). The operation of a Miller Integrator circuit is described `by B. H. Briggs in the August 1948 issue of Electronic Engineering on pages 243-247. The Miller Integrator circuit is utilized in this embodiment although other types of storage devices may be employed. A change in the voltage that is fed to the grid-cathode circuit of the Miller Integrator tube results in practically no lchange in grid voltage but in a large lineair change in plate voltage. The voltage on the anode of the Miller Integrator tube 31 with respect to the grid, or the charge stored in the condenser 32, is then an analog of the X-component of the position of the radar target, and is impressed upon one of the horizontal plates of the comparator tube 21, while the X-sawtooth 55 is impressed on the other.

Comparison Device (Comparator) The comparison device, or comparator tube 21, shown in FIGURE 3, comprises an evacuated electron beam tube including an electron gun with its associated control grid, and accelerating and focusing electrodes, all of which are represented in schematic form by a cathode 22. The comparator tube 21 also includes two pairs of orthogonal deilecting plates 23, 24, 25, and 26, a cupshaped collecting electrode 27 having an aperture in its base, and a target electrode 28 located adjacent to the aperture in the collecting electrode (cup) 27. The analog voltages derived from the X- or Y-stores 31 and 37, are applied to deilecting plates 25, `23 respectively in each of the opposed pairs of plates. The other plates 24, 26 in each pair are respectively provided with the sawtooth voltages S5 and S6 on the X-bus 16 and Y-bus 17. In the particular embodiment illustrated in FIG- URE 3, the X-voltages are coupled to the horizontal pair of deflecting plates 24 and 25, although they may be coupled to the vertical deflecting plates 23 and 26 if so desired.

During the major portion of the antennas rotation, the amplitudes of the X- and Y-sawtooth voltages 55 and 56 will differ widely from the anode voltages of the Miller Integrator Tubes 31 and 37. The electron beam from the cathode of the comparator, or gating, tube 21 will, therefore, be deflected, striking the cup 27 and passing to ground through resistor 29 connected thereto. This results in a high negative potential across resistor 29, which potential is transferred freely through diodes 47, d8, and 49 to the control grids of the electron tubes 33, 34, 35, 36, and biases these tubes far beyond cut-off.

However, when the amplitudes of the X- and Y-sawtooth voltages 55 and 56 reach substantial equivalence with the values of the X and Y analog voltages, respectively, stored in the Xland Y1-stores A31 and 37, the electron beam passes through the aperture in the collecting electrode 27 to the target plate 28. Since current no longer Hows through the resistor 29, the potential at its ungrounded end suddenly rises to a less negative value and remains there until the deflecting voltages differ suiliciently to cause the electron beam to strike the collecting electrode 27 once again, whereupon the potential at the ungrounded end of the resistor 29 returns to its former negative value. Substantial equivalence between the X-Y analog voltages and the X-Y sawtooth voltages thus results in a positive-going, gating pulse across the resistor 29'.

The size of the aperture in the collecting electrode 27 is determined by the speed of the fastest-moving target to be tracked, or, more precisely, by the distance such a target can traverse during the period of a single antenna rotation. In order for the X-Y stores 3'1 and 37 to be corrected during a second antenna rotation, a gating pulse must be generated by the X-Y comparator 21. The gating pulse can be formed only if the electron beam passes through the aperture in element 27. The aperture must, therefore, be large enough to enable the beam to be deilected through it when the difference between the data stored during a tirst antenna rotation and the new data obtained during the succeeding rotation results from the maximum movement of the speediest target to be tracked. lf the aperture were smaller than this, the difference in the voltages applied to the dei'lecting plates 23, 24, 25, and 26 of the comparator 21 would be too great to deilect the beam through the aperture, a gating pulse would not be generated and the stores 31 and 37 for that target would remain uncorrected, or, in other words, the target would not be automatically tracked, as desired.

Varableand Constant-Current Circuits Variable-current tube 34 is a tetrode biased by a combination of two voltages. The rst is the voltage across resistor 29, which is the result of the current flow from the negative supply voltage to ground through resistors 51, 50 and 29, and the current ilow through resistor 29 alone due to the electron beam from the comparator 21. The second is the voltage tapped off the voltage divider formed by resistors 40 and 41, on the high potential end of which is impressed the voltage from the X-store condenser 32 and on the low potential end of which is impressed the negative potential of the base line of the X-analog pulse.

Constant-current tube 33 whose plate is in series with the cathode of variable-current tube 34, is a pentode also biased by two voltages. The first of these is applied to the control grid and is the voltage across resistors 50 and 29 of the voltage divider comprising resistors 51, 50 and 29. The second is the negative supply voltage and is coupled to the suppressor grid through resistor 52.

The biasing of the variable-current and constant-current tubes 36 and 35 associated with the Y-store 317 is accomplished in a manner similar to that described above for tubes 34 and 313 associated with the X-store 31.

As the radar antenna sweeps toward the area in which the target was previously located, the amplitudes of the X- and Y-sawtooth voltages 55 and 56 approach equality with the amplitudes of the stored voltages of the Miller Integrator tubes 31 and 37. The electron beam then experiences very little dellecting potential and passes through the hole in the center of the cup 27 to the grounded target 28. The previous bias across resistor 29, due to the action of the electron beam, disappears,

leaving the voltage on resistor 29 only slightly negative. The diodes 4S and 47 then cease to conduct leaving the variable-current tube 34 biased beyond cut-ott only by the negative voltage that forms the base of the X-analog pulse 57, and constant-current pentode tube 33 biased beyond cut-off only by the negative voltage coupled to its suppressor grid through resistor 52. At this time, constant-current tube 33 is conducting some screen grid current, but no plate current.

Now, as the radar antenna sweeps across the target, an echo pulse is received. 'Ihe re-formed echo pulse is coupled to the suppressor grid of constant-current tube 33 and raises it above cut-olf. The function of constant current tube 33 is to conduct a constant, predetermined value of current during the time an echo pulse is being received. The negative bias on its suppressor grid through resistor 52 as reduced by the pulse from bus 20, the negative bias impressed on its control grid by the action of the voltage divider comprising resistors 51, 50 and 29, and the cathode bias generated across resistors 45 and 46 are adjusted so that this predetermined current will be maintained through constant-current tube 33 during the time the echo pulse is being received.

Simultaneously with the impression of the re-formed echo pulse on the suppressor grid of constant-current tube 33, a negative X-analog pulse 57 is impressed on bus 1.3 and thence on resistor 41. While these pulses persist, the potential on the control grid of lvariable-current tube 34 is the sum of the old analog voltage carried in store and the new negative analog voltage on bus |18. Thus, the voltage on the grid of 34 is the difference between the stored and the true analog voltages. This diierence is a measure of the correction that must be made.

Thus, when the location of the target remains unchanged, and variable-current tube 34- conducts the same amount of current as constant-current tube 33, no current will ow into the Miller Integrator storage circuit, which is eectively in shunt with constant-current tube 33, and there will be no change in the quantity of charge stored in storage condenser 32.

However, if the position of the target has changed since the last sweep of the radar antenna, the value of the X- analog pulse 57 will be different from the value of the anode fvoltage of the Miller Integrator tube 31. A net voltage, either positive or negative from its previous value, will now exist at the control grid of variable-current tube 34, causing it to conduct either more or less current than constant-current tube 33. Under these conditions, a current will yflow into or out of storage condenser 32, correcting the amount of charge stored in the condenser until it corresponds to the new X-position of the target as indicated by the value of the negative X- analog pulse 57.

The small rheostat 46 in the cathode of the constantcurrent tube 33 is provided so that the currents owing through tubes 33 and 34 may be adjusted for equality when the voltage on the grid of tube 34 indicates that no correction is needed.

iIn the description of the system, the scale of the stored voltage on the anode of the Miller Integrator tube 31 was assumed to be equal to the scale of the negative X- analog pulse voltage S7, and resistor was assumed to be equal to resistor 41. These voltage scales may be different, provided that resistors `4() and 41 are properly proportioned and the base value of the negative analog pulse 57 is suilicient to keep variable-current tube 34 biased beyond cut-ot between pulses.

The parts of the system concerned with the correction of the Y-analog voltage on the storage condenser 38 are the Miller Integrator tube 37, the constant-current tube 35, the variable-current tube 36, and their associated components, all of which correspond respectively to the following X-analog components: the Miller Integrator tube 31, the constant-current tube 33, the variable-current tube 34, and their associated components.

It is to be understood, of course, that a position-store l@ circuit, which comprises all of the components to the right of the bus bars in FIGURE 3, is required for each target which is to be tracked, and that if it is desired to store data with respect to more than one target, additional position-store circuits must be added to the system.

Target Acquisition M echansm As previously explained, once a set of stores contains X- and Y-coordinate analog voltages approximately equal to the incoming X- and Y-analog pulses, recurrent periodic correction of the stores automatically results. The problem is to initially associate a set of stores with a specic target and insert the proper analog voltages corresponding to the position of that speciic target.

Referring again to vFIGURE 2a, the outputs of all stores are coupled to the sampler 94. The invention includes a plurality of sets of stores but since they are all substantially identical only a single set, comprising .X1-store 31 and Yl-store 37, is illustrated. The sampler 94 may be a high-speed, double-pole, multi-contact, rotary switch, or an electronic switching circuit. It a rotary switch is employed as illustrated, all X-stores are coupled to one set of contacts 158, 159, i160, and all Y-stores to the other set of contacts 161, 162, 163, the X- and Y-stores of a single set being respectively coupled to identically positioned stations, or contacts, on each of the poles 164, 165. Although only three sets of contacts are illustrated it is to be understood that there are as many sets of contacts as there are sets of stores.

The X- and Y-coordinate analogs are coupled sequentially by the rotation of the contact arms 166, 167 of the switch 94 to the X- and Y- deiiection plates, respectively, of the monitor display device `92, which may be a cathode-ray display tube. The operating voltages of the monitor display tube 92 are such that the electron beam is operative at all times and forms a spot in the center of the screen of the monitor display tube 92 when zero range analog signals are applied from the X-Y stores. This will be explained subsequently in connection with the operation of the coordinate resolver 93.

The monitor display tube 92 and the radar display tube 90, on which the detected video output of the receiver 155 is displayed, are arranged at right angles to each otherl and a dichroic mirror 91 is placed at an angle of 45 with respect to each of the display tubes and 92. A dichroic mirror is a device which both transmits and reilects light that strikes it, the mirror imparting a color to the transmitted light which diiers from the color imparted to the reflected light. Thus, some light from the radar display tube 90 is transmitted through the dichroie mirror 91 to the eye of the operator and some light from the monitor display tube 92 is reected from the dichroic mirror 91 to the eye of the operator. The optical arrangement of the tubes and mirror is such that target indications on the monitor display tube 92 are superposed upon their counterparts on the radar display tube 90. However, light coming to the eye of the operator from the radar display device 90 has a different color (e.g., blue) than light from the monitor display device 92 (e.g., red).

When the radar antenna 153 rst picks up a target, it is displayed only on the radar display tube 90 and appears blue to the operator. If this target were being automatically tracked by the radar, coordinate analog voltages corresponding to its position `would be stored in a pair of X- and Y-stores and a target indication would appear on the monitor display tube 92. The dichroic mirror 91 imparts a red color to this target indication, but it is superposed upon the blue target indication of the radar display tube 90 and the combination is white to the eye of the observer. Thus, when the observer sees a white indication, he knows that the target is being automatically tracked, but when he sees a blue indication he knows that coordinate analog voltages for the target must be inserted in a pair of empty X- and Y-stores.

The operator selects a pair of X-Y stores, depresses the push-button switch 320 (FIGURE. 6) in the joystick handle 300 and then moves the handle 300 so that a target indication appears on the monitor display tube 92. He continues to move the joystick handle 300 until this target indication, which appears red to him, is superposed upon the original blue target indication. He thereupon releases the push-button switch 320, removes the joystick output from the stores, and the ATWS radar then tracks the target automatically.

Coordinate Resolver The coordinate resolver is a device by means of which direct-current analog voltages corresponding to the rectangular coordinates of the position of any target on the radar display device 90 may be derived. The particular coordinate resolver 93 employed in this embodiment comprises a joystick mechanism `which permits two perpendicular shafts to be rotated in either possible direction by `moving a single lever attached to both.

FIGURE r6 illustrates a joystick mechanism which furnishes X- and Y -rectangular coordinate voltages in accordance with the position of the joystick handle 300. The shafts 30S yand 30d are supported by four shaft supports 306 mounted on a base (not shown). The joystick handle 300 is separated into two parts by a yoke 101, to which the two parts are aixed. The lower part of the handle 300 rides in a groove between the tracks which form the X-shaft linkage 316. if the orientation of the X-shaft 305 is north-south and that of the Y-shaft 304 is east-west, the lower part of the joystick handle can move in a north or south direction in the groove of the X-shaft linkage 316.

The joystick handle 300 may also be moved in the eastwest direction by rotating its yoke 301 around a pair of pivot dowels 302 afxed to the Y-shaft coupling block 303 and extending through the yoke 301. Rotating the handle 300 in the east-west direction rotates the X-shaft 305, to the end of which a slip ring 313 is attached. An output voltage proportional to the position of the handle 300 is derived from the contact arm 308 of the X-shaft potentiometer 307, said voltage increasing in positive amplitude as the handle 300 is moved from its extreme westerly position to its extreme easterly position.

Similarly, movement of the handle 300 from south to north rotates the Y-shaft 304 and furnishes an increasing positive voltage from the Y-sha'ft potentiometer 310. The output voltages are taken from brushes 314 and 312 which contact the slip rings 315 and 313 aixed to the Y- and X-shafts 304 and 305, respectively. The X- and Y-outputs are respectively coupled through a switch 95 (see FIG. 2a) to the X- and Y-stores of one of the pairs of stores. The switch 95 may be a four-pole, multiposition, manually operated switch. In each position there are four contacts; one connected to the anode of an X-store tube; one to the grid of the same tube; one to the anode of the Y-store tube associated with said X-store tube as a pair and one to the grid of the Y-store tube. Each set of four contacts is coupled to a different pair of X-Y stores.

Thus, the X- and Y-shafts may be compared to the X- and Y-axes of a rectangular coordinate plot, and the joystick mechanism is a means of resolving the location of the top section of the joystick handle 300 with respect to the axes into X- and Y-coordinate analog voltages.

It may be noted that in the particular type of joystick mechanism indicated in this embodiment the lever can be moved directly to the desired position-thus, if the lever is in a vertical position at the origin of the X-Y coordinate axes, it could, for example be moved directly along the 45 line bisecting the angle between the X-Y axes, or in any other desired path.

As a consequence of the circuit arrangement and constants of the X- and Y-stores 31 and 37, the stored analog of the X-component of the position of a target ranges from volts for the most Westerly position to approximately +l00 volts for the most easterly position, with of a joystick mechanism.

zero range being represented by approximately +50 volts. Sirnilarly, the stored analog of the Y-component of the position of a target ranges from 0 volts for the most southerly position to approximately +100 volts for the most northerly position, with zero range being represented by approximately +50 volts. This necessitates grounding the potentiometers 307 and 310 at the points shown in FIGURE 6, so that the outputs from the potentiometers 307 and 310 vary from 0 volts to approximately +100 volts as the joystick handle 300 is moved from its most westerly (or southerly) position to its most easterly (or northerly) position.

Furthermore, in order to establish the zero range position of the electron beam of the monitor display device 92. in the center of its screen, a positive voltage equal to approximately 50 volts mu-st be applied to the pair of deflection plates on which signals from the sampler 94 are not impressed (see FIGURE 2).

The joystick handle 300 also contains a push-button switch 320, which has two poles commonly coupled to the contact arm of a potentiometer 323. One terminal 324 of this potentiometer 323 is coupled to a source of direct-current voltage more negative than that to which the cathodes of the Miller stores tubes 31 and 37 are coupled. The moving arm of the potentiometer 3'23 is adjusted so that the voltage tapped oit is equal to the grid voltage required to afford zero range output voltage from the stores 31 and 37. The output contacts of the push-button switch 320 are connected by means of flexible leads 321 to a terminal block 322 and thence through the switch 95 to the grid electrodes of the pair of X- and Y-stores selected by the switch 95.

The operator selects a pair of X- and Y-stores by operating the switch 95. He then depresses the push-button switch 320 and moves the joystick handle 300 to the correct position as previously explained. `If any charges have been retained in those stores from a previous use, the voltages now applied to the grids and anodes of the stores correct them to the values now desired. 'Fhe operator then releases the push-button switch 320 and moves switch 95 to the neutral, or off position.

It is to be noted that other means, such as a pair of independent potentiometers having their contact arms connected to ordinary knobs, may be employed in place The operator then uses his right hand to operate one knob and his left hand to operate the other.

Height Circuits The components of the height-iinding radar 128 shown in FIGURE 2b are generally similar to those of the twodimensional search radar 11. The antenna 153b, in addition to being rotated in azimuth, is also given a continuous nodding motion by the antenna height drive means 157, which may be a motor and a suitable switching circuit. The antenna 15311 scans relatively slowly upward from an approximately horizontal reference point and quickly descends after reaching a vertical limit. In a preferred `form of the invention, many vertical scans occur during the course of a single azimuthal scan.

Referring to FIGURE 7, the moving arm of a potentiometer 161 is mechanically coupled to the shaft which rotates the antenna 153b of the height-finding radar 123 through its vertical scanning motion and is arranged to provide zero output when the antenna 15319 is horizontal. As the antenna 153i) scans in the vertical direction, the output 162 of the potentiometer 161 increases in proportion to the angle of elevation. After reaching its maximum angle of elevation, the antenna 153.",` is quickly returned to its horizontal position and another vertical scan is initiated. This results in substantially a sawtooth output signal 162. from the potentiometer, the amplitude of the sawtooth 162 being proportional to the angle of elevation of the antenna 153]; at any given instant in the vertical scanning cycle.

If height of target (rather than elevation angle of antenna) data is desired, the source of direct-current voltage 160 may be replaced by the range-sweep sawtooth signals from the height-finding radar 128 and the linear-wound potentiometer 161 may be replaced by a sine-wound potentiometer.

The sawtooth signal 162 is coupled to the suppressor grid of a normally cut-off ampliier stage 163, to the control grid of which is ted constant-amplitude, positive pulses 165 which are produced whenever target echoes are received by the radar 128. These positive pulses 165 cause the amplifier 163 to conduct for the duration of each pulse. The output of the amplifier 163, which is taken from its cathode, is a positive pulse whose amplitude is determined by the amplitude of the sawtooth signal 162 on the suppressor grid. Thus, the amplitude of an output pulse of the amplifier 163 is proportional to the height of the target from whose echo it is derived.

The positive pulse input 165 to the control grid of the amplier 163 is derived by coupling the target echoes from the detector circuits in the receiver 155b to a normally cut oit threshold stage 167. The bias voltage is adjusted by a variable resistor 169 so that noise is eliminated and only target returns are amplified. The output of the threshold stage 167 is coupled to a single-shot multivibrator 166, whose output is a positive pulse of constant amplitude synchronized in time with the target echo which initiated it.

The height comparator tube 2lb is identical to that illustrated in FIGURE 3 and described previously under the subheading Comparison Device (Comparator). The analog voltages X1 and Y1 from the Xland Y1- stores 31 and 37 are applied to one deflecting plate 24h and 23b, respectively, in each of the opposed pairs of plates. The Xland Y1-analogs are direct-current voltages which may be either positive or negative in polarity. The range-sawtooth analog voltages Xs and Ys from the range coordinate resolver 12b are applied to the other deflecting plate 25h and 26h, respectively, in each of the opposed pairs of plates. In the particular embodiment shown in FIGURE 7, the X-analogs are coupled to the horizontal pair of deecting plates 24h and 25.5, and the Y-analogs are coupled to the vertical pair of deecting plates 23h and 26h, although the converse connections may be employed if so desired.

If the respective sawtooth analog voltages differ from their corresponding direct current analog voltages, the electron beam experiences deecting forces and, instead of travelling through the axially located aperture in the collecting electrode 27h, strikes the inner walls of the collecting electrode 27b. The resulting current owing through the resistor 2911 maintains the suppressor grid of the height-gate tube 180 at a negative potential. However, `when the X1- and AXS-analog voltages approach equality and simultaneously Y1- and Ys-analog voltages approach equality, the electron beam no longer strikes the inner walls of the collecting electrode 27h but passes through the aperture. With the cessation of current through the resistor 291:, the voltage at the suppressor grid of the height-gate tube 180 rises suddenly to ground potential and remains there until the analog voltages again become sufficiently unequal to cause the electron beam to strike the inner walls of the collecting electrode 27h.

Thus, the comparator tube 21b forms a positive-going, gating pulse which is coupled to the suppressor grid of the height-gate tube 186, thereby causing the latter to conduct a current in proportion to the amplitude of any height-analog pulse which may be present at its control grid at the same instant.

The voltage on its cathode when the height-gate tube 180 conducts is also proportional to the amplitude of the height-analog pulse and this cathode voltage activates a relay 182 which thereupon couples it to the heightstore 3117, which may comprise a Miller Store circuit.

14 n. STORAGE TUBE nMBoDiMENT FIGURE 8 illustrates an embodiment of the invention in which the instantaneous X- and Y-analogs, Xs and Ys, are derived from a storage tube 400. The storage tube 400 must have writing and reading means and may, for example, be a Graphechon designed for electromagnetic or electrostatic deflection. (Further details of the construction and operation of a Graphechon may be obtained on pages 5l-53 of Knoll and Kazan, Storage Tubes, published by John Wiley and Sons, New York.) Only two elements of the writing and reading guns are shown, namely cathodes 401 and 414 respectively, and accelerating anodes 402 and 413 respectively. One of the vertical deflecting plates 484 of the writing gun is connected to the Y-pole of the sampler 94a, and one of the horizontal deliecting plates 463 is coupled to the X-pole of the sampler 94a. The other horizontal and vertical detlecting plates 405 and 496, respectively, are connected to a source of positive direct-current voltage.

The sampler 94a is the same type of high-speed, doublepole, a rotary switch as the sampler 94 in FIGURE 2. The outputs of each set of X-Y stores are applied to one set of contacts on the sampler 94a, whence they are sequentially impressed on the writing-gun deflection plates 403 and 404 of the storage tube 400. Since it is desired to scan the reading beam of the storage tube 400 in PPI fashion, the targets (outputs of the X-Y stores) must be written in the same positions that they would occupy on a PPI plot with the radar in the center. However, as previously explained, the output of the stores is a positive voltage even when the range of a target is zero. To correct for this, a compensating positive voltage, suicient to place the zero range position of all radar targets at the center of the PPI plot on the target plate 420 of the storage tube 400, is provided by means of the adjustable arm of a potentiometer 407 in series with a source of positive direct-current voltage 408. Thus, as regards range and azimuth, a complete representation of the geographical positions of the targets being tracked Iby the two-dimensional radar 11 is recorded of the target plate 420 of the storage tube 409.

The reading beam is now dellected in PPI fashion in `synchronism with the azimuthal scanning of the antenna 153b of the height-nding radar 128 by means of resolved range sawtooth signals obtained from the range resolver 12b. Thus, whenever the height nding radar antenna beam strikes a target, the reading beam strikes a recorded representation of the same target in the same relative position on the target plate 420 of the storage tube 490. The reading beam output, which is a pulse of voltage, is derived from the target plate 420 and applied to a pulse-type range coordinate resolver 111 which provides rectangular pulse analogs, Xs and Ys respectively, of the east-west and north-south cartesian coordinates of the instantaneous position of the target from whose echo they are derived. It is to be noted that in the case of `a stationary target, these pulse analogs 0ccur at the precise instant the height-finding radar 128 receives its echoes `from the actual target in space from which the echoes on the target -plate 420 of the storage tube `400 were derived. The Xsand Ys-analogs are called instantaneous analogs because they are associated with the point in space for which the height-tind- 'ing radar is, at the instant of their derivation, delivering height data.

As explained previously in connection with the relationship between the size of the aperture in the collecting electrode of the X-Y comparator and the speed of the fastest moving target to be tracked, in order for gating pulses to be formed, the X-Y data obtained on the succeeding antenna rotation must not be so different from the stored X-Y data that the beam does not pass through the aperture in the collecting electrode at all. This necessitates making the size of the aperture sufficiently large that the new X-Y data (if corresponding to the farthest position which the fastest target to be tracked can attain in one antenna rotation) cannot deflect the beam enough to prevent it from passing through the aperture. The size of the aperture thus corresponds to the outer limits of the area surrounding its original position traversablc by the fastest target during one antenna rotation.

This reasoning is also valid for the size of the aperture in the H-comparator. In addition to this, when a storage tube and pulse-type range coordinate resolver is utilized for obtaining the comparison data (the instantaneous range coordinate analogs, Xs and YS, of the azimuthal position of the target), if the target echo is recorded on the storage tube as a single point, theoretically only a single pair of instantaneous pulses is obtained, with amplitudes correspon-ding to the position of the target during the previous rotation of the search radars antenna. lf the target has moved since then, the radiated beam of the height-finding radar does not strike the target at the same time that the reading beam of the storage tube strikes the recorded target echo. Thus, production of height data does not correspond in time with production of the instantaneous Xs and Ys data which gates open the height gate-and-charge circuits and the height data is not stored. This diiculty is obviated by defocusing the writing beam of the storage tube so that a target echo is written as a charged area whose limits correspond to the limits of the area traversable by the fastest moving target during one search radar antenna rotation. This permits instantaneous Xs and Ys pulses to be generated simultaneously with the production of height data for a given target, regardless of the distance the target has travelled during the previous rotation of the search radar antenna.

Pulse-Type Range Coordinate Resolver FIGURE 9 illustrates a typical circuit for a pulse-type range coordinate resolver 111. When the reading beam of the storage tube 400 traverses an echo area on the target plate 420, a video pulse output is coupled to a control grid of a multi-element tube 200 having at least two grids. The tube 200 is biased so that in the absence of a video pulse, it is in a cut-off condition. The range sweep sawtooth voltage from the height-finding radar 128 is coupled to a -second grid of the multi-element tube 200.

When a video pulse is impressed on the tube 200, it conducts and the signal across cathode resistor 261 is a pulse having an amplitude depending upont he amplitude of the range sawtooth voltage impressed on the tube 260 at that instant. Thus, the amplitude of the pulse corresponds to the range of the echo from which it is derived.

The pulse across the cathode resistor 201 is impressed upon the rotating coil (rotor) 202 of a synchro 205', which has two quadrature stationary coils (stators) 203 and 204. The rotor 202 is mechanically coupled to the antenna 1531; of the height-finding radar 128 so that it rotates in synchronism with the azimuthal rotation of the antenna 15317.

Thus, the outputs of the stators 203 and 204 will be pulses whose amplitudes vary as the sine and cosine of the azimuthal angle of rotation of the antenna 153b. These pulses are applied in common to all the H-comparators, the Xs pulse being applied to one of the horizontal deecting plates and the Ys pulse being applied to one of the vertical deflecting plates. The other horizontal and vertical deliecting plates in each H-comparator is coupled respectively to an X- and a Y-store of one of the X-Y store pairs. The comparison and gating operations of the H-comparators are identical to those of the X-Y comparators already described. It is sufficient to note that when the X- and Y-analogs stored in a pair of X-Y stores is approximately equal to the instantaneous analogs Xs land Ys derived from a target on the `storage tube target plate 420, the height analog corresponding to that target is stored in the height store associated with that pair of X-Y stores.

The electrical data stored in the height and range store circuits may be coupled to utilization means, such as kinescope display tubes or recording devices, and utilized therefrom in the control of airport traffic, or in groundcontrolled interception of aircraft; or the data may be coupled to electronic gun-laying equipment which takes the range and height data associated with a given target and utilizes this information to automatically compute firing data for anti-aircraft artillery.

Slewng System for Height Finder The slewing system to be described below is applicable both to the preferred embodiment (described under I above) and the storage tube embodiment (described under Il above).

Referring now to FIGURE l0, azimuth drive motor 350, servo amplifier 352, control transformer 354, synchro-generator 356, and the various connections to these stages are conventional. Thus, mechanical connection 358 drives the rotor of the synchro-generator. The rotor is also supplied with alternating current from a 60 cycle power source or the like (not shown). The stator of the synchro-generator may be of the conventional three phase type and is connected to a similar stator of control transformer 354. The three conductor interconnection 360 and other interconnections are shown schematically as single leads. When the rotor of the synchro-generator differs in relative position from 4that of the control transformer, the latter provides an error signal having a sense and amplitude which are functions of direction and extent of said difference in position. The error signal is amplified by servo amplifier 352 and applied to power azimuth drive motor 350. The latter rotates antenna ISSb of the height-nder in the azimuth direction at the rotational speed of mechanical connection (shaft) 358. The drive motor also is coupled via mechanical connection 352 to the rotor of the control transformer and drives the same in the proper direction to tend to reduce to zero the error signal output thereof.

Comparator tube 2lb, shown in part in FIGURE 10, is the same one shown in FIGURE 7. It will be remembered that the output `of the comparator tube is normally at a negative potential. However, when the Xs, Ys sawtooth analogs from the height-finder range resolver (12b of FIGURE 2b) are equal in amplitude to the X1, Y1 direct voltage analogs from the Miller stores (31 and 37 of FIGURE 3) a positive going enabling pulse is produced at 364.

Relay 366 is normally not energized, whereby relay contacts 368 are normally closed. Relay 366a and others (not shown) are similarly connected to the other cornparator tubes in the system. Relays 366, 366:1, etc. are connected through diodes 367, 36761, etc. to a common bus 369. The diodes are so poled that current flows through relays 370 and 371 when a pulse from any comparator tube occurs. The diodes serve to isolate relays 366, 366a, etc. from one another. One set of relay contacts 372 of relay 370 are maintained normally closed and the other set 374 normally open. Relay contacts 376 or relay 371 are maintained normally open.

Differential 380 controls the position of the rotor of synchro-generator 356. The differential is one of the type which provides a mechanical output having a rotational speed which is the difference between the two input speeds thereto. Drive motor 382 which may, for example, rotate at a speed 01 of l2 revolutions per minute (rpm.) supplies one of the inputs and drive motor 384, when operatively connected tto the differential, supplies the other of the inputs. This may, for example, be at a speed 62 of 121/10 r.p.m. However, since magnetic brake 386 is normally energized (set) and magnetic clutch 390 normally open, the differential output is normally at a speed of 91 or l2 r.p.m. Thus, the antenna normally 17 slews in azimuth at :the relatively rapid rate of 12 r.p.m.

Elevation drive motor 392 is normally not energized, whereby, in the absence of an enabling signal from comparator tube 2lb, the antenna is not nodded in elevation; Preferably, when not nodding, the antenna is maintained in one of its extreme positions. Thus, if the elevation nod angle is -40, the antenna is maintained either at 0 or 40 as will be explained more fully below.

In operation, When the height-finder antenna 15315 is slewed by drive motors 382 and 350 to the azimuth angle of a target, tube 2lb produces a positive going enabling pulse at 364. The enabling pulse charges the capacitor 365 through relay 366, whereby this relay becomes energized and its contacts 368 open. In a similar manner the enabling pulse energizes relays 370 and 371. Relay 336 (and 336:1 etc.) is a time delay relay and remains energized (contacts 368 open) for an interval of time corresponding to at least a few degrees of azimuth rotation of antenna 153b. The reason for maintaining contacts 368 open for a few degrees will be explained later. Relays 370 and 371 (which may be replaced by a single relay having three sets of contacts, if desired) are also time delay relays and remain energized for the time required for the antenna to nod once (0 to 40 or 40 to 0). It will now be seen that an enabling pulse at 364 causes magnetic brake 386 to be released, magnetic clutch 390 to become energized, and elevation drive motor 392 to nod the antenna. When the magnetic clutch is energized and the brake released, the azimuth rotational speed is reduced to 1/10 r.p.m. (02-01) which is roughly 1/2 degree per second. At the same time the antenna is nodded in elevation from 0 to 40 and stopped, or vice versa.

After the one second interval, the clutch 390 is released, the brake 386 is set and the antenna slewed in azimuth at the relatively rapid rate of 12 r.p.m. When tube 2lb or any other analagous comparator tube provides another output signal the entire process is repeated.

If during the one second interval the antenna is nodding due to the enabling pulse from comparator tube 2lb, an enabling pulse is provided by comparator tube 2lb', the action of relay 36611 through diode 367a will be to reset relay 370 to the full second interval. Thus two targets in almost the same azimuth position will be measured.

When the height-finder antenna is slowed down at the azimuth angle of a target being tracked, say the one associated with comparator tube 2lb, and makes one elevation nod, a group of enabling pulses, spaced from one another, appears at junction 364. Relays 370 and 371 are of the type which remain open for one second after the last pulse is applied to the relays. Thus, if the comparator tube were not iso-lated from relay 366 after the first enabling pulse output thereof, relays 370 and 371 would remain open for one second plus the time duration of the entire group of pulses.

The arrangement shown avoids the above difficulty. The first enabling pulse at 364 opens contacts 368 and thereby isolates relays 370 and 37 from comparator tube 21111. (Note, however, that a pulse from another cornparator tube will maintain the relays 370 and 371 closed for a longer period of time, as explained previously.) The length of time relay contacts 368 remain open is not critical since comparator tube 2lb will not produce another enabling pulse (after the group of enabling pulses) for a time equivalent to almost 360 of azimuth rotation of the height-nder radar. Thus, if desired, the relay contacts may be held open for a length of time equivalent to from several degrees to almost 360 of said rotation.

What is claimed is:

1. An automatie-track-while-scan radar system cornprising, in combination, a first radar unit, including transmitter and receiver means, for continuously supplying information as to the range and azimuth of targets in a given volume of space, a second radar unit, including second transmitter and receiver means, for supplying information as to the heights of said targets at times which normally do not coincide with the times at which the corresponding azimuth and range information is supplied; means operatively associated with one of said units for storing an .analog of the information supplied by said one unit, and means for automatically correlating the amplitude of an analog of the information supplied by the other of said units with the amplitude of said stored analog information.

2. In `a system for tracking a plurality of moving objects including at least one radar system having at least means for generating radio energy in pulse form, antenna means for radiating said energy and receiving reflected energy from irradiated objects and receiver means for amplifying and detecting said received retiected energy, in combination, means for deriving from said radar system an intermittent supply of information as to the spatial position of each of said plurality of objects, said information being in the form of X, Y and Z Cartesian coordinates of the position of each of said objects; a plurality of pairs of X and Y store circuits coupled to said derivation means, each pair for storing information indicative of the X and Y coordinates of a different one of said objects; a plurality of Z store circuits coupled to said derivation means, each for storing information indicative of the Z coordinates of a different one of said objects; means operatively associated with said radar system for initially obtaining and inserting in each said pair of X and Y stores information indicative of the magnitudes of the X and Y Cartesian coordinates of a different one of said objects; and a plurality of means, each coupled to said derivation means, to one said pair of X and Y stores, and to one of said Z stores, for comparing the intermittently derived X and Y coordinate information with all stored X and Y information, for selecting that pair of X and Y stores whose stored information is equivalent within a predetermined range, to the intermittent X and Y information with which it is then being compared and for respectively supplying to said selected pair of X and Y stores and to the Z store associated with said selected pair information indicative of a parameter of said intermittent X, Y and Z information, whereby said stored information is caused to correspond to said intermittent information.

3. in a system for tracking a plurality of moving objects including at least one radar system having at least means for generating radio energy in pulse form, antenna means for radiating said energy and receiving reflected energy from irradiated objects and receiver means for amplifying and detecting said received reflected energy, in combination, means for deriving from said radar system an intermittent supply of information as to the spatial position of each of said plurality of objects, said information being in the form of a first, a second and a third coordinate; a plurality of pairs of first and second store circuits coupled to said derivation means, each pair for storing information indicative of the first and second coordinates of a different one of said objects; a plurality of third store circuits coupled to said derivations means, each for storing information indicative of the third coordinate of a different one of said objects; means operatively associated with said radar system for initially obtaining and inserting in each said pair of first and second stores information indicative of the magnitudes of the first and second coordinates of a different one of said objects; and a plurality of means, each coupled to said derivation means, to one said pair of first and second stores and to one of said third stores, for comparing the intermittently derived rstand second coordinate information with all stored first and second coordinate information, for selecting that pair of first and second stores whose stored information is equivalent within a predetermined range, to the intermittent first and second coordinate information with which it is then being comlf3 pared and for respectively supplying to said selected pair of rst and second stores and to the third store associated with said selected pair information indicative of said intermittent first, second and third coordinates whereby said stored information is caused to correspond to said intermittent information.

4. In an automatic tracking system which includes means providing electrical data indicative of two coordinates of the positions of each of a plurality of targets, and a plurality of pairs of storage means, each pair for storing the two coordinate data for a different target, apparatus for correlating electrical data indicative of the third coordinate of the position of at least one of the targets with the stored data indicative of its other two coordinates comprising, in combination, a plurality of third coordinate data storage means, each for storing electrical data proportional to a third coordinate of a target position and each associated with a different pair of said two coordinate storage means; means for simultaneously deriving three coordinate data as to the position of said one target; and means for comparing the data in all of said two coordinate storage means with the corresponding two coordinate data for said one target and selecting the pair of said two coordinate storage means whose stored data is closest in value to that of said two coordinate data for said one target, and for applying the third coordinate data for said one target to the third coordinate storage means associated with the selected pair of two coordinate storage means.

5. In a system as set forth in claim 4, said two coordinates comprising coordinates in a plane parallel to the earths surface, and said third coordinate comprising a height coordinate.

6. Apparatus as set forth in claim 5, wherein said means for simultaneously deriving three coordinate data comprises a height-finding radar system.

7. In an automatic tracking system having means for deriving two-coordinate electrical data indicative of the azimuthal spatial positions of tracked targets with respect to the system, and a plurality of pairs of azimuthal storage means for storing said two-coordinate data, each pair of said azimuthal storage means for storing the data of a different target, apparatus for correlating height coordinate data for each tracked target with its stored azimuthal data and for storing and intermittently correcting such height data comprising, in combination: a plurality of means for storing charges proportional to height coordinate data, each height storage means associated with a different pair of azimuthal storage means, and means for deriving height coordinate data and simultaneous twocoordinate azimuthal data for at least one target, including means coupled to said azimuthal storage means for creating a charge pattern corresponding to the spatial pattern of the positions with respect to said tracking system of said tracked targets, means for deriving, at the instant height coordinate data is derived for a given target, an output signal from the charged area on said charge pattern representing that given target, and means for producing from said output signal simultaneous twocoordinate azimuthal data for that given target.

8. Apparatus as set forth in claim 7, wherein said means for deriving height coordinate data and simultaneous two-coordinate azimuthal data further includes a radar having an antenna scanning at least in azimuth, and wherein said means for creating a charge pattern includes: a storage tube having at least means producing a scanning Writing electron beam and a target plate; and means coupled to said writing-beam-producing means and to said azimuthal storage means for sequentially applying the stored data in each pair of said storage means to said storage tube, and wherein said means for deriving an output signal includes: means in said storage tube for producing a reading electron beam; and means for scanning said reading beam over said target plate in synchronism with the azimuthal scanning of said antenna.

9. Apparatus in accordance with claim 8, wherein said means for deriving height coordinate data and simultaneous two-coordinate azimuthal data further includes means for deriving from said output signal a pair of pulses whose amplitudes represent the azimuthal components of the range of the target from whose charged area -on said target plate said output signal was derived.

l0. In a system for tracking a moving object, in combination, a first azimuth-range determining radar system for supplying information in polar form as to the azimuth and slant range of said object; rst means for deriving from said polar coordinate information the corresponding two X and Y Cartesian coordinates indicative of the position in a horizontal plane of said object; means coupled to said first means for supplying information indicative of the magnitude of each said Cartesian coordinate; two store circuits coupled to said last-named means, one for each Cartesian coordinate, for storing said information indicative of the magnitude of each said Cartesian coordinate; a height finding radar system for supplying information in polar form as to the elevation angle, azimuth angle, and slant range of said object, said height finding radar being unsynchronized with said azimuthrange radar; second means for deriving from the polar information supplied by said height finding radar the corresponding X, Y and Z Cartesian coordinates indicative of the position in space of said object; a third store circuit for storing information indicative of the magnitude of said Z coordinate; and means coupled to said two store circuits, to said second means and to said third store circuit for supplying information indicative of the magnitude of said Z Cartesian coordinate to said Z store and for correcting said stored information in accordance with changes in said Z coordinate, said supply and correction means including comparison circuit means for comparing the X and Y information supplied by said first means and the X and Y coordinate information supplied by said second means and for permitting, solely when the twoy sets of X and Y information are of substantially the same magnitude, the information indicative of the magnitude of the Z coordinate to be supplied to said Z store.

l1. An automatic-track-while-scan radar system comprising, in combination, a first radar unit including transmitter and receiver means for continuously supplying information as to the ranges and azimuths of targets in a given volume of space; at least one height-finder radar unit for supplying information as to the heights of said targets in space; means for slewing said height finder radar unit from the azimuth of one target to the azimuths of other targets in azimuth sequence; and means` operatively associated with said two units for correlating the information supplied by one with that supplied by the other.

i2. An automatic-track-while-scan radar system as set forth in claim 11, further including means for storing, said correlated information.

13. An automatic-track-while-scan radar system as set forth in claim 12, further including means including said two units for periodically correcting said stored information so as to maintain it up to date.

`14. An automatic-track-while-scan radar system cornprising, in combination, an azimuth-range radar unit for continuously supplying information as to the range and azimuth of targets in a given volume of space; means for deriving from said azimuth-range information the X and Y spatial coordinates in a horizontal plane of said targets; a height-finder radar unit for supplying information as to the range, azimuth and elevation angle of said targets; means for deriving from said range, azimuth and elevation angle information the X, Y and Z spatial coordinates of said targets, Z being a spatial coordinate in a vertical plane; and comparison means operatively associated with said two units and responsive to substantial equality in the X and Y information derived from one with the X and Y information derived from the other for correlating the X and Y information derived from the azimuthrange finder unit with the corresponding Z information derived from the height-finder lradar unit.

15. An automatic-track-While-scan radar system ,comprising, in combination, an azimuth-range radar unit for continuously supplying information as to the range and azimuth of targets in a given volume of space; means for deriving from said azimuth-range information analog voltages indicative of the X and Y spatial coordinates in a horizontal plane fof said targets; a height-finder radar unit for supplying information as to the range, azimuth and elevation angle of said targets; means for deriving from said range, azimuth and elevation angle information analog voltages indicative of the X, Y and Z spatial coordinates of said targets, Z fbeing a spatial coordinate in avertical plane; and comparison meansoperatively associated with said two units and responsive to substantial equality in the X and Y analog voltages derived from one with the X and Y analog voltages derived from the other `for correlating the X and Y analog Ivoltages def rived from the azimuth-range radar unit with the corresponding Z analog voltages derived from the heightfinder radar unit. I

16. An automatic-track-while-scan radar system as set forth in claim z15 wherein said comparison means comprises a cathode ray beam device.

17. An automatic-track-While-scan radar system as set forth in claim l5, .further including means for periodically correcting the stored analog voltages to render them up-to-date.

18. An automatic-track-While-scan radar system as set forth in claim 15, further including means for slewing said height finder radar uni-t yfrom Ithe azimuth `of one target'to the azimuths of other targets in `azimuth sequence at a speed roughly comparable with the speed of rotation of said azimuth-range radar unit.

19. An automatic-track-while-scan radar system comprising, in combination, a first radar unit including an antenna which is capable of continuously scanning in azimuth lfor continuously supplying information as to the range and -azimuth of targets in a given volume of space; a second radar unit for supplying information as to the heights of said `targets in space, said second unit having a directive beam pattern `which scans in `azimuth non-synchronously With the scanning of the antenna of the first radar unit; and means operatively associated With both 22 of said units for slewing said beam pattern from the azimuth of one of said targets to the azi-muths of other of said targets in azimuth sequence independently of the scanning of said lantenna of said rst radar unit and at a speed roughly comparable with the azimuth scanning speed of said lantenna of said first unit.

20. An automatic-track-while-scan radar system comprising, in combination, a first radar unit, including transmitter and receiver means, for continuously supplying information as to the range and azimuth of targets in a given volume of space, la second radar unit, including sec# ond transmitter and receiver means, not synchronized with the iirst radar unit, for supplying information as to the heights of said targets fat times which normally do not coincide with the times at which the corresponding azi muth and range information is supplied; means operatively associated with one of said unit-s for storing analogs lof the azimuth and range information as to target positions supplied by the iirst radar unit, and means for automatically correlating the :amplitude of. an analog of the corresponding height information for the targets supplied by the second radar unit with the ampliutde of said stored analog information.

21. An automatic-track-While-scan radar system cornprising, `in combination, a rst radar unit, including transmitter and receiver means, for continuously supplying information as to the azimuth of targets in a given volume of space, a second radar unit, including second transmitter and receiver means, for supplying information as to the heights of said targets at times which normally do not coincide with thetimes at which the corresponding azimuth information is supplied, one of said radar units also supplying information as to the ranges vof said Itargets; means operatively associated With one of said units for storing an analog of the information supplied by said one unit, and means for automatically correlating the ampli- -tude of an analog of the information supplied by the other of said units with the amplitude of said stored analog information.

References Cited in the le of this patent v UNITED STATES PATENTS 2,566,331 Huber et al Sept. 4, 1951 2,709,804 Chance May 3l, 1955 2,803,819 Blair Aug. 20, 1957 

